An optical laminate having a polarizing film is placed on each of both sides of a liquid crystal cell of a liquid crystal display apparatus as a representative image display apparatus, the placement being attributable to an image-forming mode of the apparatus. The optical laminate representatively has a polarizing film obtained by causing a polyvinyl alcohol (PVA)-based film to adsorb a dichromatic substance and uniaxially stretching the film, and a protective film placed on each of both sides of the polarizing film. The polarizing film obtained by uniaxially stretching the PVA-based film representatively has a thickness of several tens of micrometers.
Meanwhile, in association with a worldwide increase in environmental awareness in recent years, an industrial product having only a small environmental load has been demanded in every field. For example, in the European Union, evaluation, application, and registration of impacts of chemical substances contained in industrial products on human health and the global environment (REACH) are required for the sake of human health and environmental protection, and boric acid, which is contained in the polarizing film, is a candidate substance to be subject thereto. Further, boric acid has a flame retardant function. Accordingly, when a boric acid content of the polarizing film is high, incineration efficiency during an incineration treatment of the optical laminate having the polarizing film which has become industrial waste is low, resulting in a large environmental load. Also in thermal recycling, which involves recovering thermal energy generated during incineration, when the boric acid content of the polarizing film is high, recycling efficiency is low. In addition, iodine is frequently used as the dichromatic substance to be adsorbed onto the polarizing film. However, when an iodine content of the polarizing film is high, a pale purple gas is discharged from a chimney of an incinerator during the incineration treatment, which makes neighborhood residents uneasy.
Thinning the polarizing film as means for solving the problems as described above inevitably reduces the boric acid content and iodine content of the polarizing film. The following method has been proposed as a method of stably producing a thin polarizing film (see Patent Literatures 1 to 3). A laminate of a thermoplastic resin substrate and a PVA-based resin layer is subjected to in-air stretching, and is then immersed in a dyeing liquid so that the thin polarizing film may be obtained. However, such method involves a problem in that optical characteristics (such as polarization degree and single axis transmittance) of the thin polarizing film to be obtained are insufficient.